The instant invention relates to an apparatus and method for generating light in the near ultraviolet to infrared range and more particularly to such an apparatus and method which utilizes a source of linearly polarized light to generate such a range of light.
There are several instances in which it is desirable to radiate samples of a substance with light in the near ultraviolet to infrared range. For example, in pollution monitoring, it may be desirable to shine such light onto a sample of ambient air or water in order to test for the type and amount of pollutants in the sample. Also, in exploration for minerals in the earth, bore holes are often drilled in order to extract samples for radiation with selected frequencies of light in order to derive information about the mineral content of the sample. A cheaper and more detailed sampling of material in the bore hole may be undertaken if a light source which emits light of the desired frequency and related testing equipment is lowered into the bore hole. This obviates the need for extracting a sample and facilitates sampling of the bore hole at selected increments.
In the above-described applications for utilizing light in the near ultraviolet to infrared spectrums, it may be necessary for the light to be emitted at a relatively inaccessible location, e.g., in a bore hole or under water. It is known that transmission of light along certain optical fibers is optimum in the 600 to 800 nanometer range. Light of a wavelength outside the optimum range is subject to attenuation. Although it may be desirable to obtain light in the range of approximately 300 to 600 nanometers at a remote location, transmission of light in such a range along an optical fiber subjects the light to a great deal of attenuation during such transmission.
It is a general object of the present invention to provide a source of light in the near ultraviolet to infrared range at a location remote from a linearly polarized light source which is used to generate such light.
It is a more specific object of the invention to provide such a method and apparatus which utilizes an optical fiber to transmit the linearly polarized light substantially at its optimum frequency for fiber transmission.
The apparatus includes a source of linearly polarized light and an optical fiber for transmitting such light therealong. A frequency-doubling crystal is positioned adjacent one end of the fiber so that such transmitted light passes therethrough. The transmitted light is substantially in the 500 to 1100 nanometer wavelength range which is optimum for transmission along the optical fiber. The transmitted light which emerges from the crystal includes light in the ultraviolet wavelength range, such light being twice the frequency of the transmitted light. The emergent near ultraviolet or ultraviolet light is shined into an organic dye of the type which fluoresces responsive to irradiation with light in certain frequency ranges. By proper selection of dyes, fluorescent light may be produced in the near ultraviolet to infrared range. The doubled light output of the crystal may be made to coincide with the absorption peak of the dye. By so doing, more doubled light will be absorbed resulting in greater dye fluorescence and in some cases lasing. A frequency-mixing crystal may be used in lieu of the frequency-doubling crystal to obtain further variation in the wavelength of the light shined into the dye.
In one embodiment of the invention, the fluorescent light emerging from the dye is passed through a conventional band pass filter to produce light in a selected relatively narrow wavelength band.
In another embodiment of the invention, mirrors are placed on opposite sides of the dye in order to generate laser light.
In still another embodiment of the invention, a mirror is placed on one side of the dye opposite a grating on the other side. Rotation of the grating varies the wavelength of light which is reflected into the dye cell and thus varies the wavelength of the laser light output.
In yet another embodiment of the invention, a pair of gratings are so utilized in order to generate laser light of two selected wavelengths.
Thus, it is a more specific object of the invention to provide a light source having a selected narrow wavelength in the ultraviolet to infrared range at a location remote from a linearly polarized light source which is used to generate such narrow wavelength light.
It is another specific object of the invention to provide such a source which emits laser light.
It is still another specific object of the invention to provide such a source which emits laser light of a selected wavelength.
It is yet another specific object of the invention to provide such a source which emits laser light having two selected wavelengths.